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Full text of "The manufacture and properties of iron and steel"

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CHAPTEE  XVI.
THE   HISTORY  AND   SHAPE   OP  THE   TEST-PIECE.
SECTION" XVIa.—Differences between the surface and the interior.—The first question in the inspection of steel is the manner in which the test-piece shall be taken. In former days it was the custom to plane or turn a piece to a standard size, and this method is still used in steel castings, for it is impossible to cast a bar of sufficiently accurate section, and it is also used in the case of forgings when it is deemed advisable to carve a piece from the finished material. In other work the test is either a part of the finished bar, as in small rounds and flats, or is cut from the member, as in angles, channels, etc. A sufficient length is taken to allow about 10 inches between jaws, and the readings are on an 8-inch length defined by marks of a center-punch.
A machined piece is generally inferior to a bar as it leaves the rolls. In tests made by the United States Government* in 1885, the machine was not powerful enough to pull a seven-eighth inch round, so that rods of this size were turned down to three-quarter inch in diameter. The comparative results are given in Table XVI-A, the figures in each case representing the average of 14 heats. The pieces cut from the seven-eighth inch bar are inferior
TABLE XVI-A.
Properties of f-inch Eounds in their Natural State, and $~inch Eounds of the Same Heats Turned Down to f-inch.
Condition, of bar.	TJlfc. strength ; pounds per square inch.	Elongation in 8 inches; per cent.	Reduction of area; per cent.
Ji inch natural.                   .....	66764	27.53	42.7
% inch turned to % inch,  .....	65038	26.30	42.0
* Report of the Naval Advisory Board,' 1885, pp. 81, 82. 318